1. Field
Example embodiments herein relate to methods of fabricating a semiconductor device having a pattern. Other example embodiments relate to methods of forming a pattern.
2. Related Art
As the integration of semiconductor devices increases, finer patterning is required. The width of a photoresist pattern capable of being realized by an exposure process may be determined according to following Rayleigh's equation,R=(k1)·(λ/NA)wherein R represents resolution, k1 represents a process constant, λ represents a wavelength of light source and NA represents a numerical aperture of lens.
To reduce the resolution, the process constant k1 should be smaller, the wavelength of light source λ should be shorter, or the numerical aperture NA of lens should be increased. To make the wavelength of light source shorter than the wavelength of KrF (248-mm) or ArF (193-mm), an exposure process using an extreme ultraviolet (EUV) having a wavelength of 13.4-nm as a light source may be necessary. The exposure process using the EUV as the light source requires a vacuum condition and a reflective photomask, which may be different from the vacuum condition and the reflective photomask used in the related art processes. The exposure equipment using the EUV as the light source is very expensive. As such, there are some troubles in making use of the exposure equipment for the exposure process at this point.
Reduction in the wavelength of light source has limits. As an alternative, solutions that increase the numerical aperture NA of lens are being developed. The numerical aperture NA of lens may be proportional to n(sin θ), where n represents a refractive index of a medium between a lens and a photoresist. As such, the resolution increases as the refractive index of the medium increases. By using this principle, an immersion lithography process is proposed. In the immersion lithography process, the exposure process may be performed to increase resolution through a medium (having a refractive index higher than that of air). Water, which has a refractive index of 1.4, has a higher refractive index than air, which has a refractive index of 1. When the exposure process is performed using water as the medium, a photosensitive polymer, a photoacid generator and a solvent (which are contained in a photoresist coming in contact with the water) may be dissolved into the water. In this case, bubbles may be generated at a boundary between the water and the photoresist layer.